Neutron stars are the cosmic leftovers of a supernova. They are only 10 miles across (very small, compared to other stars), but are very dense. In fact, they are so dense that one teaspoon of neutron star matter would weigh a billion tons!
Neutron stars are created when the immense heat and pressure causes the supernova's core to collapse in on itself for the final time. Because there is so much matter packed into a very small space, neutron stars have a very powerful magnetic field. This field is a trillion times as powerful as that of an ordinary star. The powerful magnetic field of a neutron star added to its very rapid spinning motion, produces a pulsing electromagnetic signal, which is like a radio wave. Scientists have been able to find over 400 neutron stars because of their unique energy output. Be sure to look at the picture and description below of a typical neutron star.